1. Field of the Invention
The present invention relates to an apparatus for driving the objective lens of an optical disk device, and particularly to an apparatus for driving an objective lens which is suitable for the two-dimensional drive of such an objective lens.
2. Prior Art
An objective lens is fixed at one end of a support which supports the lens. A through hole is formed at the center of the lens support. A shaft is vertically provided on a base and engaged in the through hole of the lens support. The diameter of the through hole is greater than that of the shaft and thus the lens support is slidable along the shaft and rotatable around the shaft. Therefore, the objective lens provided at one end of the lens support is rotatable around the slidable shaft and movable in the direction of the slidable shaft. The objective lens is moved in the axial direction for the purpose of focusing the light applied on the surface of an optical disk. The objective lens is also rotated around the shaft for the purpose of tracking so that a light spot is positioned in each track of the optical disk. The lens support is moved in the axial direction and rotated around the shaft by employing the functions of the magnetic field produced by a permanent magnet which is provided on the base side and the magnetic field produced by charging electricity into a coil which is provided on the drive side (lens support side). Such apparatus for driving objective lenses are disclosed in Japanese Patent Laid-Open No. 182028/1985 and Japanese Utility Model Laid-Open No. 194126/1984.
In the above-described conventional apparatus, since the lens support is movably engaged with the slide shaft, there is a space between the lens support and the slide shaft. This apparatus therefore has a problem in that, when external acceleration in the direction of tracking (rotation direction) is applied to the apparatus for driving an objective lens, the lens support is moved in the tracking direction and a light spot is also moved following this.
In order to realize high-precision tracking positioning, conventional optical disk devices utilize two-stage servo-tracking. In other words, a light spot having a low frequency and a large amplitude is moved by moving the whole of an optical head, and a light spot having a high frequency and a small amplitude is moved by moving the objective lens alone in the apparatus for driving the objective lens.
In order to realize this two-stage servo-tracking in the apparatus for driving the objective lens without using any sensor for detecting the relative position between the objective lens and the optical head, it is necessary to move the whole of the optical head and the light spot independently by solely utilizing the apparatus for driving the objective lens. Although this condition can be achieved by detecting the relative position between the optical head and the objective lens, there has been a problem with respect to the necessarily complicated structure of the optical head or the apparatus for driving the objective lens, which leads to a high cost.